This invention relates to an improved card based access control system and more particularly, to an access control system utilizing an encoded acoustic wave device in a wallet-size pass card; and, a mechanism for decoding the device.
All access control systems perform the fundamental process of verifying the eligibility of an individual seeking access to some restricted area. There are many techniques and devices used to attain various degrees of security. Many of these systems are card based and having a unique personal identification number encoded on the card itself. The most common cards are embossed plastic cards or plastic cards with magnetic tape (or a combination of both). Other less common cards are punched cards, electric circuit cards, differential optics cards, copper strip cards, and capacitance cards.
There are advantages and disadvantages to all such card-based systems. Besides obvious economic considerations, there are other important factors to consider in selecting a card entry system, such as, ease of duplicating or forging cards, number of unique ID codes possible, ease of encryption, reliability, durability and speed of operation.
Surface acoustic wave (SAW) devices configured as a tapped delay line could be used as the storage mechanism for an ID number. Such a device placed on a wallet-size plastic card would possess many desireable features if used in combination with an appropriate card reader device. Such a SAW device easily could store 30 bits of binary code in a very small area and thus accomodate a large number of potential users (2.sup.30 in excess of 1 billion). It would be difficult to counterfeit or duplicate existing cards, and a SAW device card would appear to possess other basic requirements of a card based system.